Afghan President Hamid Karzai and his Pakistani counterpart Asif Ali Zardari are set to hold key talks with British Prime Minister David Cameron on the Afghan peace process.

The summit at Cameron's Chequers country retreat near London is aimed at boosting cooperation between Afghanistan and Pakistan, amid growing fears that a civil war could erupt when international troops leave Afghanistan next year.

Support from Pakistan, which backed Afghanistan's 1996-2001 Taliban regime, is seen as crucial to peace after NATO troops depart -- but relations between the neighbours remain uneasy despite some recent improvements.